The present invention relates to a method and apparatus for diagnosing a malfunction in a clutch actuator of a motor vehicle. The clutch actuator receives an input command signal of variable magnitude from a control unit that may belong to an automatically shifting transmission, an automated clutch or a continuously variable transmission. The input command signal controls the position of the clutch actuator and thereby sets the state of engagement of the clutch. As a common trait of the inventive method as well as existing methods, the clutch-actuator position or state of engagement of the clutch is measured and an output signal corresponding to the measured actuator position is made available.
In the search for safety-monitoring concepts for automatically shifting transmissions, it has been found that many critical situations arise mainly in connection with the actuation of the clutch, e.g., if the clutch moves into or out of engagement at times when this is not intended. It is therefore of the highest importance to have real-time information about the current status of the clutch.
In connection with automatic or automated clutches or transmissions, it is a known concept to provide a measurement signal that indicates the position of the clutch actuator. However, as a matter of principle, the possibility of failure has to be taken into account for a position-sensor of the clutch actuator just as for any other technical component. Thus, the position of the clutch actuator as indicated by the sensor is not unconditionally reliable. Consequently, in connection with monitoring the safety of automated shift transmissions, it is highly advisable to include the clutch position or clutch actuator position in the monitoring process.
As an attempt to satisfy this need, a known concept of monitoring the position sensor of the clutch actuator involves a plausibility test based on minimum and maximum signal values. However, this allows only certain extreme malfunctions of the sensor to be discovered, e.g., a short circuit or a break in the cable.
The present invention therefore has the objective of providing a method of diagnosing malfunctions in a clutch actuator, whereby the position of the clutch actuator and the state of engagement of the clutch can be monitored with a higher degree of reliability in comparison to known state-of-the-art methods.
The invention further has the objective of providing an apparatus in the form of a clutch-actuating system in which the safe functioning of the clutch is assured in accordance with the inventive method.
The objective outlined above is met by the method according to the invention, as follows: The clutch actuator receives an input command signal of variable magnitude from a control unit that may belong to an automatically shifting transmission, an automated clutch or a continuously variable transmission. The input command signal controls the position of the clutch actuator and thereby sets the state of engagement of the clutch. The clutch-actuator position or state of engagement of the clutch is measured, and a position signal corresponding to the actually measured actuator position is made available. The method according to the invention is distinguished in that the aforementioned input command signal is simultaneously applied to the input of an emulation model of the actuator. The emulation model calculates a signal representing a theoretically estimated actuator position. The respective signals for the actual and theoretical actuator positions are compared to each other in a comparator unit which sends the result of the comparison to an arithmetic unit. The arithmetic unit, in turn, generates a status signal that characterizes the degree of functionality of the clutch actuator.
The object of the invention is further met by a variation of the inventive method, wherein the position signal corresponding to the measured actuator position is entered as an input into a processor unit for the function of the clutch and the dynamic behavior of the engine, which generates an rpm-signal representing the actually measured rpm-rate of the engine. The position signal corresponding to the measured actuator position is simultaneously entered as an input into a calculator unit, which generates a theoretical rpm-signal representing a theoretically estimated rpm-rate of the engine based on the position signal and the engine torque. The respective signals for the actually measured and theoretically estimated rpm-rate are compared to each other in a comparator unit which produces a comparison signal that is indicative of the functionality of the clutch actuator.
The objective stated above is also accomplished by a further variation of a method for diagnosing a malfunction of a clutch, with the following elements: A first electrical signal generated by a first sensor indicates if the motor vehicle is standing still. A second electrical signal generated by a second sensor indicates if a gear in the automatically shifting transmission cannot be synchronized within a prescribed time interval. A third electrical signal generated by a third sensor indicates if the engine is running. The first, second and third electrical signals are brought together and evaluated in a logic AND-member which sets an error flag indicating a malfunction in the clutch-actuating system if all three signals are affirmative.
As a further contribution to meet the above objective, the invention provides an apparatus in the form of a clutch-actuating system wherein the actuation of a clutch is automated and the safe functioning of the clutch is assured through the method according to the invention as described herein, including its different embodiments and variations.
The method according to the present invention has the principal advantage that it offers a far-reaching degree of detection of malfunctions of a clutch actuator in a relatively simple way by correlating the actual position of the clutch actuator as measured by a sensor with a theoretically estimated actuator position provided by an emulation model of an actuator as a function of the position-controlling input command signal.
The novel features that are considered as characteristic of the invention are set forth in particular in the appended claims. The improved apparatus itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawing.